Various multiple access schemes may be used in wireless communication systems, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), etc. These modulation schemes can increase system capacity by demodulating signals received from multiple users of a communication system.
FDMA is a channel access method used in multiple-access protocols as a channelization protocol. FDMA gives users an individual allocation of one or several frequency bands, or channels. Multiple access systems coordinate access between multiple users. These protocols are utilized differently, at different levels of the theoretical Open Systems Interconnection (OSI) model.
Single-carrier frequency division multiple access (SC-FDMA) is a frequency-division multiple access scheme. Like other multiple access schemes (TDMA, FDMA, CDMA, OFDM), it assigns of multiple users to a shared communication resource. SC-FDMA is used in some popular wireless system standards such as Long Term Evolution Advanced (LTE-A) for uplink communications. SC-FDMA can be viewed as a linearly precoded OFDMA scheme, in the sense that it has an additional Discrete Fourier Transform (DFT) processing preceding the conventional OFDM processing. Just like in OFDM, guard intervals with cyclic repetition are introduced between blocks of symbols to efficiently eliminate time spreading (caused by multi-path propagation) among the blocks.
In SC-FDMA, multiple access among users is made possible by assigning to different users different sets of non-overlapping Fourier-coefficients (sub-carriers). This is achieved at the transmitter by inserting (prior to Inverse Fast Fourier Transform (IFFT)) silent Fourier-coefficients (at positions assigned to other users), and removing them on the receiver side after the Fast Fourier Transform (FFT).